高浓度无机盐对正负离子等摩尔混合表面活性剂表面活性的影响

Effect of Salt with High Concentration on Surface Activities of Equimolar Mixtures of Cationic-Anionic Surfactants

一般认为无机盐对等链长正负离子表面活性剂等摩尔混合体系的表面活性没有明显影响 .通过测定等摩尔癸基三乙基溴化铵和癸烷磺酸钠混合体系在卤化钠 (NaX ,X =F-,Cl-,Br-,I-)溶液中的表面活性 ,发现高浓度的无机盐具有明显影响 ,使混合表面活性剂的临界胶束浓度 (cmc)降低 ,水溶液的最低表面张力 (γcmc)升高 .无机盐的影响程度随NaX中X的离子半径增加而增大 .可通过无机反离子对正负离子表面活性剂头基之间吸引作用的“屏蔽”及“盐析”

It is usually thought that inorganic salts have little effect on the surface activity of equimolarly mixed cationic-anionic surfactant mixtures. This work studied the effect of sodium halide (NaX, X=F-, Cl-, Br-, I-) on the surface activity of equimolarly mixed decyltriethylammonium bromide-sodium decanesufonate. It was showed that the added salts with high concentration had obvious effect on the surface activities, and the critical micelle concentration (cmc) was decreased, while the lowest surface tension of the aqueous solution (gamma(cmc)) was increased. Such effects were increased with ion radius of X- of NaX. The results were explained in terms of the 'screening' effect of inorganic counter ions on the attraction between oppositely charged headgroups of mixed cationic-anionic surfactants and the 'salt out' effect.